On Wed, Apr 02, 2025 at 09:19:45PM +0200, Jiri Olsa wrote:

On Wed, Apr 02, 2025 at 11:01:48AM +0200, Jiri Olsa wrote:

quoted

On Tue, Apr 01, 2025 at 03:06:22PM -0700, Andrii Nakryiko wrote:

quoted

On Tue, Apr 1, 2025 at 5:40 AM Tao Chen [off-list ref] wrote:

quoted

在 2025/4/1 19:03, Jiri Olsa 写道:

quoted

On Mon, Mar 31, 2025 at 05:47:45PM +0800, Tao Chen wrote:

quoted

The target_fd and flags in link_create no used in multi_uprobe
, return -EINVAL if they assigned, keep it same as other link
attach apis.

Fixes: 89ae89f53d20 ("bpf: Add multi uprobe link")
Signed-off-by: Tao Chen <redacted>
---
  kernel/trace/bpf_trace.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 2f206a2a2..f7ebf17e3 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c

@@ -3385,6 +3385,9 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
     if (sizeof(u64) != sizeof(void *))
             return -EOPNOTSUPP;

+    if (attr->link_create.target_fd || attr->link_create.flags)
+            return -EINVAL;

I think the CI is failing because usdt code does uprobe multi detection
with target_fd = -1 and it fails and perf-uprobe fallback will fail on
not having enough file descriptors

Hi jiri

As you said, i found it, thanks.

static int probe_uprobe_multi_link(int token_fd)
{
         LIBBPF_OPTS(bpf_prog_load_opts, load_opts,
                 .expected_attach_type = BPF_TRACE_UPROBE_MULTI,
                 .token_fd = token_fd,
                 .prog_flags = token_fd ? BPF_F_TOKEN_FD : 0,
         );
         LIBBPF_OPTS(bpf_link_create_opts, link_opts);
         struct bpf_insn insns[] = {
                 BPF_MOV64_IMM(BPF_REG_0, 0),
                 BPF_EXIT_INSN(),
         };
         int prog_fd, link_fd, err;
         unsigned long offset = 0;

         prog_fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, NULL, "GPL",
                                 insns, ARRAY_SIZE(insns), &load_opts);
         if (prog_fd < 0)
                 return -errno;

         /* Creating uprobe in '/' binary should fail with -EBADF. */
         link_opts.uprobe_multi.path = "/";
         link_opts.uprobe_multi.offsets = &offset;
         link_opts.uprobe_multi.cnt = 1;

         link_fd = bpf_link_create(prog_fd, -1, BPF_TRACE_UPROBE_MULTI,
&link_opts);

quoted

but I think at this stage we will brake some user apps by introducing
this check, link ebpf go library, which passes 0

So is it ok just check the flags?

good catch, Jiri! Yep, let's validate just flags?

I think so.. I'll test that with ebpf/go to make sure we are safe
at least there ;-) I'll let you know

sorry, got stuck.. link_create.flags are initialized to zero,
so I think flags check should be fine (at least for ebpf/go)

sry forgot.. adding Timo to the loop (ebpf/go)

jirka